Method of testing optical information medium

ABSTRACT

A testing method capable of quantifying abrasion resistance on the translucent base surface of a high-recording-density optical information medium simply and in a form of reflecting an actual application environment, and judging criteria appropriate for the testing method. When an evaluation test in terms of abrasion resistance on a laser beam incident-side surface is conducted on an optical information medium to and/or from which recording and/or reproducing is made by a laser beam shone into an information recording layer from a translucent base side, and which has the focused radius R, of a recording/reproducing laser beam on the translucent base surface, of 40-400 μm, defined by the following expression (1) R=2T tan [sin −1  (NA/n)](1) (in the expression, T is the thickness (μm) of the translucent base, NA numerical aperture of an object lens in the recording/reproducing device, and n refractive index of the translucent base), the abrasion resistance on a laser beam incident-side surface is evaluated based on the error amount of a reproduction signal after a laser beam incident-side surface is abraded by an abrasion wheel specified in ISO9352.

TECHNICAL FIELD

The present invention relates to a testing method capable of quantifyingabrasion resistance on the translucent base side surface of ahigh-recording-density optical information medium simply and in a formof reflecting an actual application environment.

BACKGROUND ART

In recent years, optical information media typified by CDs and DVDs havebeen widely used as recording media to record large-volume digital data.In general, in a reproduction-only optical information medium, atranslucent base, a reflection layer, and a protective layer arelaminated sequentially in that order from a light-incident surface side,and in a writable optical information medium, a translucent base, arecording layer, a reflection layer, and a protective layer arelaminated sequentially in that order from a light-incident surface side.

The reflection layer serves as an information recording layer in thereproduction-only optical information medium, and the recording layerserves as the information recording layer in the writable opticalinformation medium. When data is read in either of these types ofoptical information medium, a reproducing laser beam is applied from thetranslucent base side, and the reflected light thereof is detected. Whendata is written into the writable optical recording medium, a recordinglaser beam is applied from the translucent base side, and the chemicalstate or the physical state of the recording layer is changed by thethermal energy and/or the light energy of the laser beam based on thedata to be recorded.

Here, the laser beam applied to the optical information medium isfocused with an optical system in such a way that a beam spot having apredetermined radius is formed on the reflection layer or the recordinglayer. Consequently, if there is a flaw on the surface of thetranslucent base, the beam spot is not formed properly, and a read errorand a write error may occur. A method in which a high-hardness hard coatlayer is disposed on the surface of the translucent base has beenpreviously known as a method for preventing occurrence of such a flaw.

In recent years, attempts have been made to increase the numericalaperture (NA) of an object lens used for focusing therecording/reproducing laser beam to on the order of 0.85, and reduce thewavelength λ of the recording/reproducing laser beam to on the order of400 nm, so as to make the focused spot radius small and, thereby, recordlarge-volume digital data. As a result, recently, a next-generationoptical disc format has been made public under the designation ofBlu-ray Disc.

Such an increase in NA causes reduction in allowance for warp andinclination, that is, tilt margin, of the optical information medium.Therefore, in order to ensure an adequate tilt margin, the thickness ofthe translucent base must be decreased. For example, when NA is set aton the order of 0.85 and λ is set at on the order of 400 nm, it isrequired to decrease the thickness of the translucent base to on theorder of 100 μm in order to ensure the adequate tilt margin.

Furthermore, the increase in NA causes reduction in working distancebetween an object lens and the surface of the optical recording medium.For example, when NA is set at on the order of 0.85, the workingdistance is decreased to on the order of 100 μm significantly smallerthan ever.

However, when the working distance is significantly decreased, there isa very high possibility that the surface of the optical informationmedium and the object lens or a support supporting the object lens arebrought into contact with each other during the rotation of the opticalinformation medium. If such a contact occurs during the rotation of theoptical information medium, a fatal flaw may occur on the translucentbase surface of the optical information medium. The occurrence of a flawresulting from such contact can be prevented to some extent by disposingthe above-described hard coat layer. However, in the case where thethickness of the translucent base is decreased to on the order of 100μm, the focused radius of the recording/reproducing laser beam on thetranslucent base surface is also decreased significantly. Therefore,even a flaw of the size not causing a read error or a write error inknown optical information media, e.g., CDs and DVDs, readily cause aread error or a write error. Consequently, a hard coat exhibitingperformance higher than ever is required.

The focused radius R of the recording/reproducing laser beam on thetranslucent base surface is ideally represented by the followingexpression (1):R=2T tan [sin⁻¹(NA/n)]  (1)(in the expression, T is the thickness (μm) of the translucent base ofthe optical information medium, NA is the numerical aperture of theobject lens in the recording/reproducing device of the opticalinformation medium, and n is the refractive index of the translucentbase of the optical information medium).

Therefore, as for a DVD in which NA=0.60 and T=0.6 mm, when n is assumedto be on the order of 1.58, R becomes on the order of 500 μm. On theother hand, as for a system in which NA=0.85 and T=100 μm, R becomes onthe order of 130 μm, and the focused spot radius on the translucent basesurface becomes significantly small.

Such a significant decrease in focused spot radius on the translucentbase surface refers to that the sensitivity to not only a flaw resultingfrom the contact with the object lens, but also a flaw resulting fromhandling by the user is extremely enhanced. From this point of view aswell, the performance of the hard coat must be significantly improvedthan ever.

With respect to optical information media, such as a Blu-ray Disc,having a focused spot radius on the translucent base surfacesignificantly smaller than that of a known optical information medium,the abrasion resistance on the translucent base surface must beevaluated by some way in the case where an appropriate hard coatmaterial is selected in the process of development, or in the case wherequality control is performed in the process of production. However,under present circumstances, there is no appropriate means thereforeother than the method for evaluating an optical information mediumdescribed in Japanese Unexamined Patent Application Publication No.2002-260280 which was applied for a patent by the applicant of thepresent invention and was laid open.

In general, when the abrasion resistance on paint coatings and resinmaterials are evaluated, in many cases, sample surfaces are abraded bypredetermined abrasion devices, and the amounts of abrasion of testpieces resulting therefrom are quantified by using the amounts of changeof various parameters, e.g., mass, thickness, and light transmittance ofthe test piece. As for optically translucent materials, such as a hardcoat layer material of the optical information medium, having relativelyhigh surface hardnesses, it is most appropriate to quantify by using theamount of change in light transmittance or light diffusion. One of thereasons therefore is that the amount of abrasion is not large to theextent capable of being indicated by the amount of change in mass orthickness of the test piece. Specifically, it is generally performedthat white parallel light is allowed to incident on the above-describedtest piece and the haze value thereof is measured.

However, since the evaluation method based on the measurement of theabove-described haze value is a method in which transmitted light of thetranslucent test piece is measured, the method cannot be applieddirectly to the translucent base surface of the optical informationmedium.

Another problem occurs in that the determination of appropriate judgingcriteria of abrasion resistance is difficult in itself with respect tothe translucent base surface of the high-recording-density opticalinformation medium, e.g., a Blu-ray Disc. As for optical informationmedia, e.g., CDs and DVDs, which have been already commercialized andbecome widespread, there are track records of usage by many users.Therefore, the judging criteria of the level of abrasion resistance onthe surface of the translucent base required for preventing occurrenceof any problem in the daily use can be determined based on those trackrecords. However, as for the significantly high-recording-densityoptical information media, e.g., a Blu-ray Disc, that is, opticalinformation media in need of high-performance hard coat layer materials,there is no track record of usage by the user. Consequently, it takessome period of time until an adequate track record of usage isestablished. Therefore, the judging criteria of the level of abrasionresistance required for preventing occurrence of any problem in practicecannot be determined based on the actual track records of usage byusers.

Accordingly, it is an object of the present invention to provide atesting method capable of quantifying abrasion resistance on atranslucent base surface of a high-recording-density optical informationmedium simply and in a form of reflecting an actual applicationenvironment, and to provide judging criteria appropriate for the testingmethod.

DISCLOSURE OF INVENTION

The inventors of the present invention conducted intensive research toovercome the above-described problems. As a result, it was found outthat there was a good correlation between the extent of abrasion of ahigh-recording-density optical information medium in which the surfacewas abraded by a predetermined method and the error amount of areproduction signal after abrasion, so that the present invention hasbeen completed.

A method of testing an optical information medium according to thepresent invention is a method of conducting an evaluation test in termsof abrasion resistance on a laser beam incident-side surface of theoptical information medium which includes at least a support base, aninformation recording layer, and a translucent base in that order, toand/or from which recording and/or reproducing is made optically by alaser beam incident on the above-described information recording layerfrom the above-described translucent base side, and which has thefocused radius R of a recording/reproducing laser beam of 40 μm or moreand 400 μm or less on the above-described translucent base surface, thefocused radius R defined by the following expression (1):R=2T tan [sin⁻¹(NA/n)]  (1)(in the expression, T is the thickness (μm) of the translucent base ofthe optical information medium, NA is the numerical aperture of anobject lens in the recording/reproducing device of the opticalinformation medium, and n is the refractive index of the translucentbase of the optical information medium), the method characterized bycomprising the step of

evaluating the abrasion resistance on the laser beam incident-sidesurface based on the error amount of a reproduction signal after theabove-described laser beam incident-side surface is abraded by abrasionwheels specified in ISO9352.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view showing an example of configurationof a high-recording-density optical information medium according to thepresent invention.

FIG. 2 is a graph representing the relationship between the number ofabrasion cycles and the PI error value of a DVD-ROM.

FIG. 3 is a graph representing the relationship between the number ofabrasion cycles and the bit error rate in Test examples 3 to 8.

FIG. 4 is a graph representing the relationship between the number ofabrasion cycles and the haze value (%) in Test examples 9 to 11.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be specifically describedbelow.

In the present invention, a laser beam incident-side surface of atargeted optical information medium is abraded by abrasive wheelsspecified in ISO9352. This abrasive device can effect abrasion with ahigh degree of reproducibility.

Here, the testing method for abrasion resistance by abrasive wheelsspecified in ISO9352 is a testing method generally referred to as aTaber abrasion test. In this method, a tester is used in which twogrinding wheels referred to as abrasive wheels are disposed atpredetermined positions on a turntable, and a sample is placed on thisturntable. Subsequently, a predetermined load is applied to the wheels,and the turntable is rotated by a motor. At this time, the abrasivewheels are configured to grind the sample surface while keeping aconstant inclination relative to the rotation direction of theturntable.

Several types of abrasive wheels, which are different in materials andgrain sizes, are prepared. The abrasion resistance on the opticalinformation medium subjected to the test can be made clear byappropriately selecting the type of the abrasive wheel, the load appliedduring abrading, the number of revolutions of the turntable, and thelike. In the present specification, the number of abrasion by abrasivewheels and the number of revolutions of the turntable are in the samesense.

Preferably, the type of the abrasive wheel to be used is any one ofelastic abrasive wheels CS-10, CS-10F, and CF-17, and more preferably,CS-10F is used. Preferably, the turntable is rotated to effect abrasionwith a load of 2.5 N or more and 4.9 N or less. More preferably, theturntable is rotated to effect abrasion with a load of 2.5 N. In thismanner, the abrasion speed can be reduced, the number of revolutions ofthe turntable can be increased, and the test accuracy can be increased.The abrasion speed can be further reduced when suction through anabrasion powder suction nozzle is not performed.

In the testing method of the present invention, the optical informationmedium having been abraded as described above is evaluated directly withan optical disk driving device.

The inventors of the present invention ascertained that in the testingmethod of the present invention, the error amount of a reproductionsignal to be measured exhibited a high correlation with flaws on thetranslucent base surface of the optical information medium. When thiserror amount is small, for example, recorded moving images and the likecan be reproduced without occurrence of any problem. In the case where abit error rate (bER) is used as an index of the error amount, thethreshold value of a general optical information medium is specified tobe on the order of 1×10⁻⁴ regardless of the type thereof. Therefore, inthe testing method of the present invention, the abrasion resistance onthe laser beam incident-side surface of the optical information mediumcan be evaluated by measuring the number of abrasion by abrasive wheelsuntil the bER reaches this threshold value. Specific examples of usableindices of the error amount include a bite error rate (BER) and an erroramount index measured in accordance with the method for measuring anerror specified in the specification of each optical information mediumin addition to the bER.

Each of the above-described judging criteria is based on the followinggrounds.

In the testing method of the present invention, the optical informationmedium to be tested is primarily assumed to be a high-recording-densityoptical information medium in which the wavelength λ of therecording/reproducing laser beam of 600 nm or less and the numericalaperture NA of an object lens of 0.7 or more, that is, an opticalinformation medium having the focused radius R of 40 μm or more and 400μm or less, the R represented by the above-described expression (1).Such an optical information medium has not been commercialized as ofnow, and even if it is commercialized in the near future, a considerableperiod of time will be needed to widespread in the market. Therefore,the specification of the level of abrasion resistance on the translucentbase surface of the optical information medium itself to be tested, theabrasion resistance required to prevent occurrence of any problem inpractice, cannot be determined based on the track records of usage ofthe optical information medium.

Therefore, in the testing method of the present invention, the judgingcriteria thereof are determined based on the optical information mediumhaving been already widespread in the market. In the present invention,a digital versatile disk (DVD) is used as the reference.

DVDs include reproduction-only DVD-ROM, write once (recording ispossible only once) DVD-R and DVD+R, and rewritable (recording ispossible repeatedly) DVD-RW, DVD+RW, and DVD-RAM. All these opticaldisks include polycarbonate substrates formed by injection molding astranslucent bases. In many cases, hard coat layers are disposed on thesurfaces of the above-described polycarbonate substrates in therewritable DVD-RW, DVD+RW, and DVD-RAM. In general, acrylic ultravioletcuring resins are used as the materials for the hard coat layers. On theother hand, in the reproduction-only DVD-ROM and the write once DVD-Rand DVD+R, no hard coat layer is disposed in principle, and thepolycarbonate substrate is exposed at the translucent base surface.

These are not stored in cartridges, and are used in the condition asthey are (hereafter referred to as bare disk) with the exceptions of apart of DVD-RAM and the like. That is, it can be considered that usersrecognize bare disks of all optical information media belong to theabove-described DVD format as disks having no problem in practiceregardless of whether a hard coat layer is disposed on the translucentbase surface thereof or not.

The evaluation method of the present invention is applied to ahigh-recording-density optical information medium in which at least asupport base, an information recording layer, and a translucent base,and a laser beam is incident on the information recording layer from theabove-described translucent base side, so that recording and/orreproducing is made optically. Specific examples of configurations ofthe above-described optical information medium include a configurationshown in FIG. 1. In the optical information medium shown in FIG. 1, areflection layer 5, a second dielectric layer 32, a recording layer 4serving as an information recording layer, a first dielectric layer 31,a translucent base 21, and a hard coat layer 22 are disposed in thatorder on one surface of a support base 20. The translucent base 21 is aresin layer formed by affixing a resin sheet or applying an ultravioletcuring resin. The laser beam for recording and/or reproducing isincident on the recording layer 4 through the translucent base 21. Themedium having the structure shown in FIG. 1 is suitable for high-densityrecording since the translucent base 21 can be made thin and, thereby,the medium can be compatible with an increase in NA of an object lens ofa recording/reproducing optical system. In the structure shown in FIG.1, preferably, the total thickness of the translucent base 21 and thehard coat layer 22 is 50 to 300 μm, more preferably is 80 to 120 μm. Ifthis thickness is too small, an optical influence of dust attached tothe laser-beam incident-side surface of the medium is increased. On theother hand, if this thickness is too large, an allowance for inclination(tilt margin) of the disk surface relative to the recording/reproducinglaser beam cannot be ensured.

The optical information medium shown in FIG. 1 includes an ultravioletcuring resin film, in which inorganic fine particles are dispersed, asthe hard coat layer 22 on the laser beam incident side of thetranslucent base 21. Consequently, the hardness is adequately high, andexcellent wear resistance and abrasion resistance are exhibit. In anoptical disk system which has a high NA and to which the medium shown inFIG. 1 is applied, since the translucent base 21 is thin, an influenceof the presence of flaws on the surface of the translucent base 21 isincreased. Therefore, the ultraviolet curing resin film, in whichinorganic fine particles are dispersed, is particularly suitable forsuch an optical information medium.

Preferably, the thickness of the ultraviolet-cured resin film, in whichinorganic fine particles are dispersed, is 0.5 μm or more, and morepreferably is 1.0 μm or more. If the above-described cured film is toothin, an adequate wear-resistant effect cannot be achieved.

The ultraviolet-cured resin film, in which inorganic fine particles aredispersed, is formed by applying an ultraviolet curing resin, in whichinorganic fine particles are dispersed, or a solution thereof on thelaser beam incident-side surface of the translucent base 21 and curingit by ultraviolet irradiation after heat-drying is performed, ifnecessary. Examples of inorganic fine particles include silica, alumina,zirconia, titania, Sn-doped indium oxide (ITO), and Sb-doped tin oxide(ATO). Among the inorganic fine particles, reactive silica particlesdescribed in, for example, Japanese Unexamined Patent ApplicationPublication No. 9-100111 are suitable for use in the present invention,where the reactive silica particles are particles in which fine particlesurfaces are modified by compounds having active energy raypolymerizable groups and which are fixed in a resin matrix after thereaction. The abrasion resistance on the hard coat layer can be furtherenhanced by adding the above-described inorganic particles in a hardcoat agent composition. The content of the inorganic particles is, forexample, about 5 to 80 percent by weight in the hard coat agentcomposition (as a solid content in the case where a non-reactive diluentis contained). If the content of the inorganic particles exceeds 80percent by weight, the brittleness of the hard coat layer tends to bedeteriorated.

Preferably, the translucent base 21 is composed of a thermoplasticresin, e.g., polycarbonate or polymethylmethacrylate (PMMA), or anactive energy ray curable resin, e.g., acrylic ultraviolet curing resin.

The ultraviolet curing resin film containing dispersed inorganicparticles can realize alone a film having extremely high wearresistance. However, another layer may be disposed on the cured filmsurface, if necessary. Preferably, another layer is a functional layerhaving at least one function selected from the group consisting of thelubricity, the antistatic property, the antireflection property, thewater repellency, and the oil repellency.

The present invention will be described below with reference to theexamples.

TEST EXAMPLES 1 AND 2

(Medium Sample 1)

A DVD-ROM (commercial item) in which no hard coat layer was included andpolycarbonate was adopted as a translucent base was used as Mediumsample 1 to be tested, and an evaluation test of the abrasion resistancethereof was conducted as described below.

The Medium sample 1 was placed on an optical recording medium evaluationdevice, and the PI error value was measured with the optical recordingmedium device (DDU1000 produced by Pulstec Industrial Co., Ltd.) and adecoder produced by Kenwood Corporation on the condition of laserwavelength: 650 nm, laser power: 1.0 mW, numerical aperture NA of objectlens: 0.60, and linear velocity: 3.5 m/s.

Subsequently, this Medium sample 1 to be tested was set on a Taberabrader and a laser beam incident-side surface of the Medium sample wasabraded by using abrasive wheels CS-10F on the two different conditions,with a load of 2.5 N and with a load of 4.9 N. Suction of abrasionpowder was not conducted when the load was 2.5 N, and the suction wasconducted only when the load was 4.9 N. The relationship between thenumber of abrasion (the number of revolutions of a turntable) and themeasurement result of the PI error value (count/8 ECC) at each of thenumbers of abrasion is shown in the following Table 1 and FIG. 2.

TABLE 1 The number Test example 1 Test example 2 of abrasion 4.9N 2.5N(time) (with suction) (without suction) 0 0 0 2 282 151 4 409 247 6 —295 8 — 350 10 — 375 (PI error value)

As is clear from the above-described Table 1 and FIG. 2, the number ofabrasion required until the threshold value is exceeded in Test example2 is larger than that in Test example 1 and, therefore, Test example 2shows a better result on the quantitative evaluation of the abrasionresistance on the laser beam incident-side surface of thehigh-recording-density optical information medium.

TEST EXAMPLES 3 TO 8

Medium samples 2 to 4 having the structure shown in FIG. 1 were preparedin a procedure as described below.

(Medium Sample 2)

The reflection layer 5 made of Al₉₈Pd₁Cu₁ (atomic ratio) having athickness of 100 nm was formed by a sputtering method on the surface ofthe support base 20 (made of polycarbonate, diameter 120 mm, andthickness 1.1 mm) provided with a groove. The depth of theabove-described groove was set at λ/6 in terms of an optical path lengthat a wavelength λ=405 nm. The recording track pitch in the grooverecording system was set at 0.32 μm.

The second dielectric layer 32 of 20 nm in thickness was formed on thesurface of the reflection layer 5 by the sputtering method through theuse of an Al₂O₃ target. The recording layer 4 of 12 nm in thickness wasformed on the surface of the second dielectric layer 32 by thesputtering method through the use of an alloy target made of a phasechange material. The composition (atomic ratio) of the recording layer 4was specified to be Sb₇₄Te₁₈(Ge₇In₁). The first dielectric layer 31 of130 nm in thickness was formed on the surface of the recording layer 4by the sputtering method through the use of a ZnS (80 percent bymole)—SiO₂ (20 percent by mole) target.

Subsequently, a radical polymerizable ultraviolet curing resin havingthe following composition was applied by a spin coating method to thesurface of the first dielectric layer 31, and an ultraviolet ray wasapplied, so that the translucent base 21 was formed in such a way thatthe thickness after curing became 98 μm. Composition of translucentbase: ultraviolet curing resin

urethane acrylate oligomer 50 parts by weight (DIABEAM UK6035 producedby MITSUBISHI 10 parts by weight RAYON CO., LTD.) isocyanuric acid EO-modified triacrylate (ARONIX M315 produced by TOAGOSEI 5 parts by weightCo., Ltd.) isocyanuric acid EO- modified diacrylate (ARONIX M215produced by TOAGOSEI 25 parts by weight Co., Ltd.) tetrahydrofurfurylacrylate photopolymerization initiator (1- 3 parts by weighthydroxycyclohexylphenyl ketone)

Furthermore, an ultraviolet curing hard coat agent having the followingcomposition was applied by a spin coating method to the translucent base21, so that a coating was formed. A diluent in the coating was removedby heating in the air at 60° C. for 3 minutes. Thereafter, anultraviolet ray was applied, so that the hard coat layer 22 of 2 μm inthickness was formed.

Composition of hard coat agent

reactive group modified colloidal silica 100 parts by weight (dispersionmedium: propylene glycol monomethyl ether acetate, nonvolatile content:40 percent by weight) dipentaerythritol hexaacrylate 48 parts by weighttetrahydrofurfuryl acrylate 12 parts by weight propylene glycolmonomethyl ether acetate 40 parts by weight (non-reactive diluent)Irgacure 184 (polymerization initiator) 5 parts by weight(Medium Sample 3)

The reflection layer 5 made of Al₉₈Pd₁Cu₁ (atomic ratio) was formed by asputtering method on the surface of the support base 20 (made ofpolycarbonate, diameter 120 mm, and thickness 1.2 mm) provided with agroove. The depth of the above-described groove was set at λ/6 in termsof an optical path length at a wavelength λ=405 nm. The recording trackpitch in the groove recording system was set at 0.32 μm.

The second dielectric layer 32 of 20 nm in thickness was formed on thesurface of the reflection layer 5 by the sputtering method through theuse of an Al₂O₃ target. The recording layer 4 of 12 nm in thickness wasformed on the surface of the second dielectric layer 32 by thesputtering method through the use of an alloy target made of a phasechange material. The composition (atomic ratio) of the recording layer 4was specified to be Sb₇₄Te₁₈(Ge₇In₁). The first dielectric layer 31 of130 nm in thickness was formed on the surface of the recording layer 4by the sputtering method through the use of a ZnS (80 percent bymole)—SiO₂ (20 percent by mole) target.

Subsequently, a radical polymerizable ultraviolet curing resin (SK5110produced by Sony Chemicals Corporation) was applied by a spin coatingmethod to the surface of the first dielectric layer 31, so that a resinlayer was formed.

A polycarbonate sheet (thickness 100 μm) was placed on the resin layerin a vacuum (0.1 atmospheres (10 kPa) or less). PUREACE produced byTeijin Limited through a flow casting method was used as theabove-described polycarbonate sheet. The atmosphere was returned to theair, and an ultraviolet ray was applied to cure the above-describedresin layer, so that the translucent base 21 was formed.

(Medium Sample 4)

An ultraviolet curing resin (SD318 produced by DAINIPPON INK ANDCHEMICALS, INCORPORATED) in place of the hard coat agent of Mediumsample 2 was applied by a spin coating method in such a way that thefilm thickness after curing became 2.5 μm, followed by curing, so thatthe hard coat layer was formed. The other steps were similar to those inMedium sample 2.

The recording layer of each of Medium samples 2 to 4 was initialized(crystallized) by a bulk eraser. Thereafter, the sample was placed on anoptical recording medium evaluation device, and a (1,7)RLL modulationsignal was recorded in a region having a radius of 37 to 38 mm on thecondition of laser wavelength: 405 nm, laser power: 5.0 mW, numericalaperture NA of object lens: 0.85, and linear velocity: 5.3 m/s. Therecorded signal was reproduced at a laser power of 0.4 mW, and a biterror rate (bER) was measured.

Three portions were arbitrarily selected from the region having a radiusof 37 to 38 mm of the disk, and the bER was measured as a signal errorrate when a signal sequence substantially corresponding to a lap (42msec) was read. An average value of bERs of the above-described threeportions was taken as the measurement result. The optical diskevaluation device (DDU1000 produced by Pulstec Industrial Co., Ltd.) wasused for the measurement.

Subsequently, each of the above-described Medium samples was set on aTaber abrader. A laser beam incident-side surface of each sample wasabraded by using abrasive wheels CS-10F on the two different conditions,with a load of 2.5 N and with a load of 4.9 N. Suction of abrasionpowder was not conducted when the load was 2.5 N, and the suction wasconducted only when the load was 4.9 N. The relationship between thenumber of abrasion (the number of revolutions of a turntable) and themeasurement result of the bit error rate value (bER) at each of thenumbers of abrasion is shown in Table 2 and FIG. 3. The value in Table 2and FIG. 3 indicates a value derived from multiplying the bit error rate(bER) by 10⁷ (seventh power of 10). As for the notational convention,“1.0E+01” represents 10. When a code on the right of E is “+”, 10 isindicated, and when a code on the right of E is “−”, one-tenth ( 1/10)is indicated. That is, “1.0E+02” represents 100, and “1.0E−02”represents one-hundredth ( 1/100).

TABLE 2 Test Test Test Test Test Test example 3 example 4 example 5example 6 example 7 example 8 Medium Medium Medium The sample 2 sample 3sample 4 number of 2.5N 4.9N 2.5N 4.9N 2.5N 4.9N abrasion (without (with(without (with (without (with (time) suction) suction) suction) suction)suction) suction) 0 1 1 1 1 1 1 2 — — 5.67 × 10⁴ 1.8 × 10⁴ — — 4 — —1.27 × 10⁵ 2.5 × 10⁵ — — 6 1.33 15.3 2.47 × 10⁵ 3.45 × 10⁵  31.3 90 1018 243 — — 50.7 3.06 × 10³ (bER × 1.0E+07value)

As is clear from the above-described Table 2 and FIG. 3, the number ofabrasion required until the threshold value is exceeded in Test examples3, 4, 7, and 8 are larger than those in Test examples 5 and 6.Therefore, Test examples 3, 4, 7, and 8 show better results in thequantitative evaluation of the abrasion resistance on the laser beamincident-side surface of the high-recording-density optical informationmedium.

TEST EXAMPLE 9 TO 11

The difference in abrasion speed based on whether abrasion powder wassuctioned through the abrasion powder suction nozzle or not was examinedin such a way that Medium sample 2 was used, white parallel light wasallowed to incident thereon, and the haze value thereof was measured.Medium sample 2 was set on a Taber abrader. A laser beam incident-sidesurface of the sample was abraded by using abrasive wheels CS-10F on thedifferent three conditions, with a load of 2.5 N (in the case whereabrasion powder was suctioned and in the case where abrasion powder wasnot suctioned) and with a load of 4.9 N (in the case where abrasionpowder was suctioned). The relationship between the number of abrasion(the number of revolutions of a turntable) and the haze value (%) ateach of the numbers of abrasion is shown in FIG. 4. As is clear fromthis FIG. 4, the abrasion speed can be favorably reduced when suctionthrough the abrasion powder suction nozzle is not performed.

INDUSTRIAL APPLICABILITY

As described above, according to the testing method of the presentinvention, even a high-recording-density optical information medium ismore sensitive to flaw and stain on the translucent base surface thanever before, the abrasion resistance on the recording/reproducing lightincident-side surface thereof can be quantified simply and in a form ofreflecting an actual application environment.

1. A method of testing an optical information medium, the methodconducting an evaluation test in terms of abrasion resistance on a laserbeam incident-side surface of the optical information medium whichincludes at least a support base, an information recording layer, and atranslucent base in that order, to and/or from which recording and/orreproducing is made optically by a laser beam incident on theinformation recording layer from the translucent base side, and whichhas a focused radius R of a recording/reproducing laser beam of 40 μm ormore and 400 μm or less on the translucent base surface, the focusedradius R defined by the following expression (1):R=2T tan [sin⁻¹(NA/n)]  (1) (in the expression, T is the thickness (μm)of the translucent base of the optical information medium, NA is thenumerical aperture of an object lens in the recording/reproducing deviceof the optical information medium, and n is the refractive index of thetranslucent base of the optical information medium), the methodcomprising: evaluating the abrasion resistance of the laser beamincident-side surface based on an error amount of a reproduction signalafter the laser beam incident-side surface has been abraded by abrasivewheels specified in ISO9352.
 2. The method of testing the opticalinformation medium according to claim 1, wherein a load of the abrasivewheels is specified to be 2.5 to 4.9 N.
 3. The method of testing theoptical information medium according to claim 1, further comprising:abrading the laser beam incident-side surface using the abrasive wheelsspecified in ISO9352.
 4. The method of testing the optical informationmedium according to claim 1, wherein the evaluating comprises evaluatingthe abrasion resistance of the laser beam incident-side surface based ona bit error rate of the reproduction signal.
 5. The method of testingthe optical information medium according to claim 4, wherein theevaluating comprises measuring a number of abrasions by the abrasivewheels until the bit error rate reaches 1×10⁻⁴.
 6. The method of testingthe optical information medium according to claim 1, wherein theevaluating comprises evaluating the abrasion resistance of the laserbeam incident-side surface based on the error amount of the reproductionsignal after each of a plurality of abrasions of the laser beamincident-side surface.
 7. A method of testing abrasion resistance of anoptical information medium including a support base, an informationlayer, and a translucent base, the method comprising: abrading a laserbeam incident-side surface of the optical information medium;reproducing data stored on the information layer by a laser beamincident on the information layer from the translucent base side, afterthe abrading; generating a reproduction signal based on the reproduceddata; and evaluating the abrasion resistance of the laser beamincident-side surface based on an error amount of the generatedreproduction signal.
 8. The method of testing abrasion resistance of theoptical information medium according to claim 7, wherein the evaluatingcomprises evaluating the abrasion resistance of the laser beamincident-side surface based on a bit error rate of the reproductionsignal.
 9. The method of testing abrasion resistance of the opticalmedium according to claim 7, wherein the evaluating comprises evaluatingthe abrasion resistance of the laser beam incident-side surface based onthe error amount of the reproduction signal after each of a plurality ofabrasions of the laser beam incident-side surface.